Phonemes are distinct units of sounds (made up of a letter or letters).  Having phonemic awareness means you can easily identify and name each sound for each letter of letters.  When you connect phonemes together, you create words.  For dyslexics, this can be hard.  With the Orton-Gillingham method, it is important that the student can recall sounds quickly in order to read more fluently.  Using a systematic letter naming technique, the student is exposed to each vowel and consonant sound repetitively in order for it to become automatic.